Forums

Transformer Question

Started by Unknown February 2, 2017
You should not make an isolation transformer your self if you don't have extensive experience 

Isolation transformers must have double insulated design which involves special copper wire, creepage and clearance distances and using approved materials for the bobbin etc

Regards 

Klaus 
whit3rd wrote:

> That might be disappointing; microwave transformers never operate without a full load, > so the possibility exists that a light load on the composite would saturate one, and get very lossy. > > Magnetic parts of a transformer have to be sized according to the MINIMUM load current.
Why do you think so? To the first approximation, the flux does not depend on the load and it is the flux that saturates the core. Best regards, Piotr
Piotr Wyderski wrote:

> > > > > Magnetic parts of a transformer have to be sized according to the MINIMUM load current. > > Why do you think so? >
** Because it is 100% correct for most applcations - dickhead.
> To the first approximation, the flux does > not depend on the load
** Fuck the "first approximation" madness.
> and it is the flux that saturates the core. >
** And is at its very worst with no load. You don't know anything about transformers. .... Phil
On Saturday, February 4, 2017 at 12:51:36 AM UTC-8, Piotr Wyderski wrote:
> whit3rd wrote:
> > Magnetic parts of a transformer have to be sized according to the MINIMUM load current. > > Why do you think so? To the first approximation, the flux does > not depend on the load and it is the flux that saturates the core.
The core is magnetized by AC current in the primary, minus the AC current of the secondary. Drawing secondary current means the magnetic core is subjected to lower fields (lower peak magnetization), which keeps it out of saturation. It's a first-order effect. When no current is delivered by the secondary windings, the minimal transformer that works well in a microwave oven might pop fuses at every transient on the AC line, or overheat. The magnetron heater always draws current, and the HV always draws current after a second or three of heating, when the microwave oven is ON and the transformer under power.
Phil Allison wrote:

> ** And is at its very worst with no load. > > You don't know anything about transformers.
Go and learn something, Allison, it is never too late. http://www.ibiblio.org/kuphaldt/electricCircuits/AC/AC_9.html In the steady state operation the magnetizing flux in the core is almost constant with respect to the load changes. In practice it is indeed highest at no load, but the difference is several percent, so meaningless. If your transformer saturates at no load, it is already broken by design. What can be a problem is the inrush current, but it is not related to the copper, but to the wrong direction of the remanent flux in the core, which depends on the material. And now you may kiss my ass.
whit3rd wrote:

> The core is magnetized by AC current in the primary, minus the AC current of the > secondary.
Yes, but the value of the primary current in the linear region depends directly on the secondary current (the Lenz rule) and the fluxes oppose each other, so their difference in the ideal transformer remains constant and equal to the flux induced by the primary's magnetizing current. It's the MMF that changes with load, not the flux. In practice there is a dependence (and has the direction in agreement with your statement), but it is small for a transformer with reasonably low winding resistances, several percent. Now if you want to design a real transformer intended to be connected to mains in the Europe, you must conform to IEC 60038:1999, which says that the input voltage is in the range of 230V+6%-10%. And since the flux directly depends on the coil's voltage, you must already design it to survive 253V AC, with zero safety margin. In practice the margin will be at least another 5%, which puts the load-related flux changes in the noise. > Drawing secondary current means the magnetic core is subjected to
> lower fields (lower peak magnetization), which keeps it out of saturation.
But no sane person would design a transformer to be 3% below the saturation knee of the B-H curve at full load. The saturation is mostly caused by bad luck with the sign of the remnant flux with respect to the current phase of the mains voltage. Or do I underestomate the Chinese 'savings'? Best regards, Piotr
whit3rd wrote:

> > > The core is magnetized by AC current in the primary, minus the AC current > of the secondary. Drawing secondary current means the magnetic core is > subjected to lower fields (lower peak magnetization), which keeps it out of > saturation. > > It's a first-order effect. >
** Fraid that is not correct. Core magnetisation depends on the applied primary AC voltage, minus any IR drop due to magnetisation current OR reflected secondary current. So the greater the load current, the less the magnetisation current. Microwave trannies depend on this fact. .... Phil
Piotr Wyderski is a fucking MORON 

> > Phil Allison wrote: > > > ** And is at its very worst with no load. > > > > You don't know anything about transformers. > > > In the steady state operation the magnetizing flux in the > core is almost constant with respect to the load changes. >
** Only true for trannies that do NOT saturate when off load. Like microwave types and most external adaptor trannies. YOU FUCKING TENTH WIT !!!!!!!!!
> > In practice it is indeed highest at no load, but the > difference is several percent, so meaningless. >
** You have NO FUCKING IDEA what the actual variations are.
> If your transformer saturates at no load, it is already broken > by design. >
** Pure asinine fuckwittery. As proven by all microwave trannies.
> What can be a problem is the inrush current, but it is > not related to the copper, but to the wrong direction > of the remanent flux in the core, which depends on > the material. >
** More absolute fucking BOLLOCKS. I reckon you are a slimy, 15 year old pig who fucks his 10 year old sister. Or you did so back when that age. Betcha. .... Phil
Phil Allison wrote:

This is a public Usenet group, not the Allisons family reunion,
where this level of coprolalia might be appropriate. The bad news for
you is that Tourette syndrome is currently incurable.

> Like microwave types and most external adaptor trannies.
The microwave transformers are called so just by convention, in reality they are pretty complex LR circuits, exactly as an AA battery is not a battery at all. Same with welding 'transformers'. A transformer is a constant flux magnitude device. Learn to live with it or give the world a relief. Same with the magnetizig current, which, by definition, is the primary current *at no load*, so it cannot decrease with load, moron.
> I reckon you are a slimy, 15 year old pig who fucks his 10 year old sister. > > Or you did so back when that age.
Yet another projection of the Allisons sexual habits. You must have had a terrible childhood. A direct hit in the head by a V2 rocket when in cradle or a Trinity test dummy?
"Piotr Wyderski" <no@mail.com> wrote in message 
news:o744mk$4ma$1@node1.news.atman.pl...
> Why do you think so? To the first approximation, the flux does > not depend on the load and it is the flux that saturates the core.
Hmm, I would say zeroeth approximation. The first order correction then includes primary winding DCR. Simple linear stuff. Higher orders are then more complicated. Load current is reflected in the primary circuit, which causes a voltage drop across DCR, therefore reduces the EMF applied to the core. Higher order corrections would be asking, is the core nonlinear under this condition? (Yes: reducing the applied voltage by, say, 5%, will result in mu_eff being slightly different, so the magnetizing current won't be proportionally smaller, but may be larger or smaller.) Is the DCR nonlinear (no -- or at least, no 2nd or 3rd order reason to suspect it), or is DCR an accurate representation? (It isn't -- ACR is necessary, particularly for very thick wire, or at higher frequencies, or harmonics.) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com